The present invention relates to polyurethane formulations including a delayed action catalyst. The present invention particularly relates to polyurethane formulations including a delayed action catalyst useful for preparing polyurethane backed textiles.
It is known in the art of preparing textile articles to use polyurethanes as backings in various forms. For example, U.S. Pat. No. 4,296,159 to Jenkines, et al., discloses preparing a tufted or woven article having a unitary backing prepared by applying a polyurethane forming composition to the underside of the tufted or woven article. A different form of polyurethane backing is disclosed in U.S. Pat. No. 5,102,714 to Mobley, et al. wherein the polyurethane backing is a tacky adhesive. It is also known to use polyurethane foam as a cushioning textile backing, as in, for example, U.S. Pat. No. 4,853,280.
The equipment used to prepare polyurethane backed textiles, particularly carpets can be both large and expensive. Therefore, generally, a polyurethane formulation used in carpet manufacturing must be made to accommodate the built in application and cure condition limitations of that equipment and not vice-versa. For example, if a particular piece of carpet backing equipment permits a post application cure of from 1-2 minutes, a formulation having 3 minute cure requirement cannot be used.
One particularly persistent problem with utilizing polyurethane backings in carpet applications is the problem of premature gellation during the polyurethane reaction. Polyurethanes are made by a wide variety of processes differing in detail. However, the basic urethane-forming reaction is the result of contact between an active-hydrogen containing compound, frequently a polyol, i.e., a dihydroxy- or poly-hydroxy compound, and a diisocyanate or polyisocyanate. The reaction of these starting materials normally requires the presence of a catalyst. A number of catalysts for this purpose are known. Among those most frequently used are tertiary amines, such as, for example, triethylene diamine and N-substitute morpholines; tin(II) salts of organic acids, such as for example tin(II) octoate; and heavy metals, such as mercury.
In the case of the tertiary amines and tin(II) salts, the catalysts serve to immediately or almost-immediately promote the reaction between the starting materials and thus may perform satisfactorily where processing requires rapid initiation of the reaction. But for some purposes, it is often desirable to delay the reaction and therefore lengthen the time between contact of the components and gelation, thereby achieving greater processing latitude. This is especially desirable in polyurethane carpet backing applications wherein once the gellation begins, the reaction preferably proceeds very rapidly. Greater processing latitude is useful in accommodating the built-in limitations of textile backing application equipment.
Some catalysts exhibit certain disadvantages that may limit their use. The amines and tin salts may result in premature gelation where processing requires additional time following contact between the starting materials. Such may be the case in the preparation of certain polyurethanes such as foams, elastomers, coatings and adhesives, where the formulation components are mixed and then the mixture is poured into a mold or onto a substrate and dispersed before gelation desirably occurs.
It is sometimes desirable to employ alternative, so-called "delayed action" catalysts, such as the heavy metals. But catalysts containing heavy metals, such as mercury, bismuth, barium or cadmium, may present toxicity and environmental safety problems that are difficult to overcome. These catalyst also may not be able to generate a sufficiently quick reaction for preparing carpets once gellation begins to meet the requirements of applying polyurethane backings to textiles.
One method of preventing premature gelation without relying on heavy metals is disclosed in U.S. Pat. No. 3,661,885 to Haddick. That invention is drawn to the use of a preformed complex of a tin(II) salt and an organic complexing agent. But the use of such compounds is not trouble free. The tin(II) salt/amine complexes tend to decompose in the presence of water, which results in loss of catalytic activity. Furthermore, the delay may be insufficient to allow for optimum processing and product quality. Thus, their applicability is somewhat limited.
Therefore, it would be desirable in the art to prepare polyurethane backed textiles with polyurethane formulations which include a delayed action catalyst. It would also be desirable if those catalysts produce both a long delay followed by a quick and complete polyurethane reaction after the onset of gellation. Also desirable would be the avoidance of using particularly toxic compounds as the catalysts.